A diesel engine has a self-ignition system. Specifically, a fuel is introduced, i.e., supplied into a combustion chamber of the engine, and then, air with the fuel in the combustion chamber is compressed so that a temperature in the combustion chamber increases. Thus, the air with the fuel having high temperature is self-ignited. It is a main issue for the diesel engine to reduce generation of toxic substance in exhaust gas. Specifically, in order to perform combustion appropriately for reducing the toxic substance, atomization and spray penetration of the fuel, which is injected from a fuel injection nozzle, are much important for the diesel engine. Further, in view of reducing smoke in the exhaust gas discharged from the diesel engine, the atomization and spray penetration of the fuel are important.
To promote the atomization of the fuel and to increase the spray penetration of the fuel, a fuel injection nozzle having multiple injection holes is provided. This nozzle includes multiple injection holes having a small diameter, which are arranged close together so that the injection holes provide one fuel spray, i.e., one fuel jet. Specifically, each injection hole injects the fuel so that a fuel jet is generated. Then, the fuel jets injected from the injection holes are integrated so that one fuel jet is formed. This nozzle is disclosed in, for example, JP-A-H07-167016 and JP-A-H09-088766.
Since multiple injection holes in the above nozzle jets, i.e., sprays, the fuel, a diameter of each injection hole can be smaller. Thus, the fuel is atomized, i.e., a fuel jet sprayed from each injection hole is atomized. Further, by interacting fuel jets injected from the injection holes, the spray penetration of the fuel jet is obtained.
The above multiple injection hole type fuel injection nozzle is, for example, a parallel center axis type nozzle, a diffusion type nozzle or a collision type nozzle. The parallel center axis type nozzle has multiple injection holes, center axes of which are in parallel together. The diffusion type nozzle has multiple injection holes, center axes of which are opened, i.e., broaden. The collision type nozzle has multiple injection holes, center axes of which are closed, i.e., narrowed.
In the parallel center axis type nozzle, interaction among the fuel jets becomes small, so that fuel spray travel (spray tip length), i.e., a reaching distance of the fuel jet becomes short. Thus, the air in the combustion chamber of the engine is not sufficiently mixed with the fuel jet. Accordingly, the smoke in the exhaust gas generates, as shown in FIG. 9B.
Here, another parallel center axis type nozzle is provided. In this nozzle, a distance between adjacent two injection holes (i.e., injection hole distance L) is short. The interaction of the fuel jets becomes large, so that the spray penetration of the fuel jets is obtained. However, in this nozzle, fuel concentration near the center of the fuel jet axis is increased, so that a part of the fuel jet having a high fuel concentration burns. Accordingly, the smoke may generate from combustion of the part of the fuel jet, as shown in FIG. 9A.
In the diffusion type nozzle, since the interaction between the fuel jets sprayed from the injection holes becomes small, the fuel spray tip length of the fuel jet becomes short. Accordingly, the smoke may generate from combustion of the part of the fuel jet, as shown in FIG. 9B.
In the collision type nozzle, the fuel jets from the injection holes strike, i.e., intersect or cross each other. Therefore, the spray penetration along with the fuel injection axis becomes small. Thus, the fuel spray tip length of the fuel jet becomes short. Further, the interaction of the fuel jets becomes strong, so that the fuel concentration near the center of the fuel jet axis is increased. Accordingly, the smoke may generate from combustion of the part of the fuel jet, as shown in FIG. 9B.
Here, in FIGS. 8 to 9B, VIIIA represents a first region (i.e., an initial injection region) of the fuel jet just after the fuel is injected from the nozzle. VIIIB represents a second region (i.e., an atomization and evaporation region) of the fuel jet after the fuel jet expands in the initial injection region VIIIA. Then, VIIIC represents a third region (i.e., a preliminary mixture region) of the fuel jet after the fuel jet expands in the atomization and evaporation region VIIIB. Then, VIIID represents a fourth region VIIID (i.e., a combustion region) after the fuel jet expands in the preliminary mixture region VIIIC.
In the prior art, the spray penetration and the atomization of the fuel have a trade-off relationship. Accordingly, it is difficult to valance the spray penetration and the atomization. In view of this problem, a new fuel injection nozzle in a fuel injection valve of direct injection engine having a self-ignition system is requested. In the new fuel injection nozzle, the spray penetration of the fuel jet jetted from the new injection nozzle is appropriately controlled so that the air disposed in a combustion chamber from the outlet of an injection hole of the new injection nozzle to an inner wall of the chamber burns with the fuel jet sufficiently. Further, combustion of the air with the fuel jet substantially ends before the fuel jet reaches the inner wall of the chamber.
Specifically, it is requested for a new fuel injection nozzle to control atomization and spray penetration of a fuel jet appropriately so that the combustion of the air with the fuel jet is completed sufficiently.